In order to study the diet composition and quantity of Coilia mystus,1 355 stomach samples of C.mystus collected from Yangtze River Estuary and Hangzhou Bay from June to August in 2009 were analyzed in this paper.The feeding amount of Copepoda ranged from 0.10 ind/fish to 3.31 ind/fish in North Channel,Changxing Island,Shanghai,while 0.06-0.23 ind/fish in South Passage,Jiuduansha Wetland,Shanghai,which indicated that the feeding intensity of C.mystus in spawning ground was relatively higher than that during migration.It's detected that the amount of Mysidacea was about 0.40 ind/fish in 100--150 mm size classes,and 0.10 ind/fish in 150-190 mm ones,which demonstrated that there was no obvious tendency of preying bigger Mysidacea by C.mystus in bigger size classes.Besides,the relationship between amount distribution of Copepoda and the size classes of C.mystus was not evident.Mysidacea was found both in stomachs of C.mystus and water samples collected from Hangzhou Bay,while there was a little amount of Mysidacea in C.mystus and none in water samples collected from Yangtze River Estuary.This showed that different composition of diet organism in various waters was the primary reason for the variety of C.mystus feeding components.It's also found that C.mystus showed a preference for Calanus sinicus(I = 0.89) and Acanthomysis longirostris(I = 0.86),while C.mystus had no active selectivity for dominant species in waters,such as Schmackeria poplesia(I =-0.39,Y = 0.30).